1. Field of the Invention
This invention relates to a digital implementation of a sigma-delta modulator. More particularly, this invention relates to a sigma-delta modulator used as a portion of a digital-to-analog conversion (DAC) circuit, where the modulator converts a multi-bit digital input signal to a 1-bit digital output signal.
2. Brief Description of the Related Technology
Sigma-delta modulators are preferred in DAC circuits because of their inherent feasibility to be manufactured in integrated circuits. These sigma-delta modulators typically convert a multi-bit input signal to a 1-bit output signal. This quantization, if performed by merely truncating or rounding the multi-bit input signal, would introduce a large amount of noise in the signal passband, thereby destroying the signal quality. Additionally, the sigma-delta modulator for the DAC circuit must filter out of band noise from the signal being converted, via a noise transfer function for the modulator, and must manipulate the signal being converted, according to a predetermined signal transfer function.
A digital sigma-delta modulator system design for shaping noise in a DAC circuit is described in application Ser. No. 08/333,386, filed Nov. 2, 1994, entitled "Digital Noise Shaper For D/A Circuit", assigned to the common assignee of the present invention.